Pressure and current responsive protection device for a cascaded transformer arrangement



I Jan. 30, 1968 K|ND 3,366,838

. PRESSURE AND CURRENT RESFONSIVE PROTECTION DEVICE FOR I A GASCADED TRANSFORMER ARRANGEMENT Fild' 0013. '7, 1965 I INVENTORY Dieter Kind ATTORNEY assists ice Patented Jan. 30, 1968 3,366,838 PRESSURE AND CURRENT RESPONSIVE PRO- TECTEON DEVICE FOR A CASCADED TRANS- FORMER ARRANGEMENT Dieter Kind, Braunschweig, Germany, assignor to Messwandler-Bau G.m.b.H. Filed Oct. 7, 1965, Ser. No. 493,831 Claims priority, application Germany, Nov. 3, 1964,

, M 62,974 8 Claims. (Cl. 3117-45) This invention relates to cascade transformers and, more particularly, to protective devices for the same.

As is known, cascade transformers for high and very high voltages have a considerable structural height. For reasons inherent in the manufacture of such transformers and particularly to facilitate their transportation, they are normally divided into two or more sections corresponding to the arrangement of the cascade stages from the viewpoints of the transformer and insulation technology. These sections are completely self-contained, or separated, electrically and with respect to the liquid therein, are individually transported, and are placed on top of one another and connected with one another only at the construction site.

If one desired to equip such a cascade transformer with a protective device responding to an undue pressure rise in its interior, whose response is to be recognizable even without direct optical observation from the operational behavior of the transformer or by an electrical signal, one could think of providing each cascade section with such a protective device. However, it must be considered that the protective devices of the upper cascade member or members are at high voltage potential, while the indication of the response of the protective device corresponding to the movement of a monitoring member must be transferred to ground potential. In order to avoid this difliculty, it has been proposed to provide a pressure monitor only in the lowest cascade member and, when assembling the sections, to establish a connection between the chambers of the liquid in the upper cascade member or members and those of the lowermost section so that by means of this pressure monitor provided at this section the liquid chambers of all of the cascade sections can be controlled. The establishment of such a connection, for example a tube connection, at the construction site of the cascade transformer is cumbersome and disadvantageous particularly because there is the danger that during the connecting operation insulating fluid can escape and air enter the liquid chambers of the individual sections.

It is accordingly an object of this invention to provide an improved protective device for cascade transformers which avoids the above described difliculties and disadvantages.

The invention relates to a protective device for a gasor liquid-insulated cascade transformer, consisting of two or more sections which are completely closed-off or separated from one another from the viewpoints of gas and liquid, are provided with tight coupling coils, and are connectable with one another electrically in the manner of a cascade circuit. According to the invention, each cascade section is provided with a pressure monitor responding to undue pressure variations, particularly increases in pressure in its interior, this pressure monitor, when responding, interrupting the connection of the tight coupling coil of the respective cascade section with the tight coupling coil of the adjacent cascade section. As is known, when, in a cascade transformer, the circuit of the tight coupling coils is opened, the secondary voltage falls, when the transformer is under load, to a fraction of its rated value; i.e., the interruption of the circuit of the tight coupling coils is noticeable on the secondary side of the cascade transformer. Since the pressure monitor can be arranged in each cascade section in the region of the potential at which the respective tight coupling coil is located, no insulating path is necessary between the pressure monitor and the switching member in the circuit of the tight coupling coil to be actuated by the monitor. Preferably, the pressure monitor is provided in the lowermost section of the cascade transformer at the top thereof, and in the uppermost section in the bottom thereof. In the case of a cascade transformer consisting of more than two sections, the central section, or sections, are provided each with two pressure monitors of which one is arranged at the top, and the other at the bottom of the respective section. Furthermore, it is especially advantageous if there are provided, in a conventional manner, in the circuit of the tight coupling coils, in addition to the circuit breakers controlled by the pressure monitors, means, for example safety fuses or devices triggered by excess current which respond to the strong increase of the current in the circuit of the tight coupling coils upon the occurrence of a short circuit in the windings or layers of a high voltage coil (see German Patent No. 1,030,445).

In the case of three cascade transformers, which are part of a symmetrical three-phase system, an interruption in the circuit of the tight coupling coils of one of the transformers can be determined simply by providing each of the transformers with an auxiliary winding, which is arranged either beside the secondary winding of the cascade transformer or is the secondary winding of an auxiliary transformer whose primary winding is supplied with current by the secondary winding of the cascade transformer, and by connecting these three auxiliary windings combined in an open delta with a device for indicating errors and/or for the emission of a switching signal.

The foregoing and other objects, advantages, and features of the invention and the manner in which the same are accomplished will become more readily apparent upon consideration of the following detailed description of the invention taken into conjunction with the accompanying drawing, which illustrates a preferred and exemplary embodiment and wherein the single figure is a schematic diagram of an embodiment of the invention.

The cascade transformer consists, for example, of two sections I and II which are completely closed off from each other from a fluid point of view. These sections are transportable independently of each other and are placed on top of each other at the construction site. They are then connected with each other mechanically as well as electrically in cascade circuit manner.

The housing of the upper cascade section I comprises an insulating jacket 11 (for example a porcelain frame) having a metallic head 12 and a metallic base 13 and is filled with insulating fluid. In this housing, an iron core 14 is provided with a high voltage coil 15 and a tight coupling winding 16. The housing of the cascade section II, likewise comprises an insulating jacket 17 having a head 18 and a base 19, and contains an iron core 26 with a tight coupling winding 21, a high voltage coil 22, and a secondary winding 23 to which a transformer load 24 is connected. In the housing of section I, a switch 25 is inserted in the connection line between the two tight coupling windings 16 and 21, this switch being opened upon an undue increase in pressure in the interior of the cascade section I by a pressure monitor 25a; and in the housing of section II, a switch 26 is provided which is opened upon an undue pressure increase in the interior of cascade section II, likewise by a pressure monitor 26a. Since the pressure monitors may be of any known type ordinarily used as protective devices against undue increases in pressure or, if desired, against undue decreases in pressure in connection with electrical devices filled with gas or insulating fluid, such as, for example, transformers, measuring transformers, and capacitors, which actuates a switch for the emission of an indicating signal or control signal for turning the device off, it is not necessary to explain their construction and mode of operation. It will be observed that the connection line containing switches 25 and as is at the potential of the connection line of the two high voltage coils l and 22, i.e., at half the highest voltage potential of the transformer. Accordingly, pressure monitor a pertaining to the switch 2.5 is provided at the bottom of the housing of cascade section I, preferably in base 13, while pressure monitor as, pertaining to the switch is provided at the top of the housing of cascade section ll, preferably in the head 18. Each disturbance occurring at the cascade section I or at the cascade section II leading to an undue increase in pressure in the interior of the respective section is thus determinable by the protective device of the invention because of the interruption of the circuit of the tight coupling windings at 25 and 26, respectively, on the secondary (low voltage) side of the cascade transformer.

As indicated in the drawing, an excess current trigger device 27 can be provided in a conventional manner in the circuit of the two tight coupling windings L3 and 21 in addition to the switches 25 and 26, this device responding to an excess current occurring in the circuit of the tight coupling windings and interrupting the connection of the two tight coupling windings 16, 21; this excess current device is suitably provided on the outside of the housing at the base 13 or at the head 18. Such an excess current will occur in the case of a short circuit of the windings or the layers of a high voltage coil of the cascade transformer and will vary in magnitude with the completeness of the short circuit in the defective high voltage coil. In this construction of the protective device, there are thus determined not only disturbances causing an undue pressure increase in the interior of the cascade sections, but also such defects at the high voltage coils which no not immediately lead to an undue pressure increase.

In the drawing, there is further exemplified how an interruption in the circuit of the tight coupling windings can be determined particularly simply in case of three cascade transformers pertaining to a symmertical threephase system. The illustrated transformer having the sections 1 and II pertains, for example, to phase R; of the other two cascade transformers of phases S and T, constructed identically, there are only shown, for the sake of simplicity, the secondary terminals u x, and M x, as well as the loads 28 and 29 connected to these terminals. Each of the three cascade transformers has assigned thereto an auxiliary transformer which is suitably housed in the base of the lower cascade section. The primary windings 3d, 31, 32 of the auxiliary transformers are connected to the secondary terminals of the three cascade transformers, while the secondary windings 33, 34, 35 are connected together in an Open delta and supply a device 36 for error indication and/or for emitting a switching control signal with power. As soon as the circuit of the tight coupling windings is interrupted in one or several of the three cascade transformers, which are under load and fixedly grounded, the vector sum of the voltages at the three secondary windings 33, 34, 35 of the auxiliary transformers, which ordinarily is equal to zero, no longer equals zero and a voltage appears at the open delta circuit, effecting the response of the device 36. In place of three auxiliary transformers, it is also possible to employ a three-phase transformer with a free ground connection in the same circuit. Such transformers are conventional in networks which are not fixedly grounded for an indication of ground leakage.

In some cases, a fixed basic load may be connected to the secondary windings of the three cascade transformers so that the breakdown of the secondary voltage of one of the transformers causes an unbalance which is suffrciently recognizable even when the transformers are idle, or have only a small load.

If response of the device 36 when a momentary short circuit to ground occurs in one of the three phases which will lead to an immediate shutdown in case of fixedly grounded networks, is to be prevented, this can be accomplished by the incorporation of a response delay member into the device 36.

The pressure monitors provided according to the invention in each cascade section can also be fashioned in such a manner that they not only respond to undue pressure increases, but also to undue pressure decreases, interrupting the circuit of the tight coupling windings. The use of such pressure monitors is recommended particularly in the case of cascade transformers which are insulated by pressurized gas, for in such transformers it is important to interrupt the tight coupling circuit in case of an undue decrease in pressure in one of the cascade sections and thus to effect an indication or a switching command.

While a preferred embodiment of the invention has been shown and described, it will be apparent to those skilled in the art that changes can be made without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims. Accordingly, the foregoing embodiment is to be considered illustrative rather than restrictive of the invention and those modifications which come within the meaning and range of equivalency are to be included therein.

The invention claimed is:

T1. A protective device for a gasor fluid-insulated cascade transformer comprising a plurality of stacked sections which are completely closed oti or separated from one another from a gas or fluid point of view, these sections being provided with tight coupling windings and being connected electrically in accordance with the eascade circuit manner with a tight coupling winding of one section being connected to a tight coupling winding of an adjacent section; said device being characterized in that each cascade section is provided with a pressure monitor responding to undue pressure variations in the interior of the section, and the connection between the tight coupling windings includes a circuit breaker, said pressure monitor, when responding to said undue pressure opening said circuit breaker in the connection between the tight coupling winding of the respective cascade section with the tight coupling winding of the adjacent cascade section.

2. A protective device according to claim ll, characterized is that the pressure monitor is provided, in case of the lowermost cascade section, in its head, and in case of the uppermost cascade section in the base thereof.

3. A protective device according to claim 1, characterized in that said cascade transformer comprises more than two section and the central section or sections are provided with respectively two pressure monitors of which one is provided in the head and the other in the base of the respective section.

4. A protective device according to claim 1, characterized in that means are provided in the circuit of the tight coupling windings, in addition to said circuit breaker, for responding to any excess current that might occur in the circuit of the tight coupling windings.

5. A protective device according to claim 1, wherein three of said cascade transformers are connected in a symmetrical three-phase system, said device comprising means for determining an interruption of the circuit of the tight coupling windings of one of the three transformers, said means being characterized in that an auxiliary winding is assigned to each of the three transformers coupled to the secondary winding of the cascade transformer and a device for providing an error indication or control signal is connected with these three auxiliary windings in an open delta.

6. A protective device according to claim 5 wherein said auxiliary Winding is the secondary Winding of an auxiliary transformer whose primary Winding is coupled to the secondary Winding of the cascade transformer.

7. A protective device according to claim 5, characterized in that the device for providing an error indication or control signal is equipped With a response delay memher.

8. A protective device according to claim 5, characterized in that a fixed basic load is connected to the secondary windings of the three cascade transformers.

UNITED STATES PATENTS Hart 317-44 X Putman 317-14 X Barr 317-14 Sauer 31715 X MILTON O. HIRSHFIELD, Primary Examiner. 10 R. V. LUPO, Assistant Examiner. 

1. A PROTECTIVE DEVICE FOR A GAS- OR FLUID-INSULATED CASCADE TRANSFORMER COMPRISING A PLURALITY OF STACKED SECTIONS WHICH ARE COMPLETELY CLOSED OFF OR SEPARATED FROM ONE ANOTHER FROM A GAS OF FLUID POINT OF VIEW, THESE SECTIONS BEING PROVIDED WITH TIGHT COUPLING WINDINGS AND BEING CONNECTED ELECTRICALLY IN ACCORDANCE WITH THE CASCADE CIRCUIT MANNER WITH A TIGHT COUPLING WINDING OF ONE SECTION BEING CONNECTED TO A TIGHT COUPLING WINDING OF AN ADJACENT SECTION; SAID DEVICE BEING CHARACTERIZED IN THAT EACH CASCADE SECTION IS PROVIDED WITH A PRESSURE MONITOR RESPONDING TO UNDUE PRESSURE VARIATIONS IN THE INTERIOR OF THE SECTION, AND THE CONNECTION BETWEEN THE TIGHT COUPLING WINDINGS INCLUDES A CIRCUIT BREAKER, SAID PRESSURE MONITOR, WHEN RESPONDING TO SAID UNDUE PRESSURE OPENING SAID CIRCUIT BREAKER IN THE CONNECTION BETWEEN THE TIGHT COUPLING WINDING OF THE RESPECTIVE CASCADE SECTION WITH THE TIGHT COUPLING WINDING OF THE ADJACENT CASCADE SECTION. 